I have a Triangle Tube Prestige Excellence 110 Boiler in an unheated basement. The issue only occurs in the winter months, currently in the 30's for outside temp. The hot water works well until 10-15 minutes in filling a bath then turns cold. Turning off the water for 5 minutes gives me a few minutes of hot water which eventually turns ice cold again.

Is there anything I can do to get this to run consistent hot water in the cold months?

We install and service Triangle Tube Excellence boiler here in St. Paul, MN and find them like any other "Combi" boiler/water heater...of limited use. That is, one must carefully size any combi-heating appliance to cover both the space heating load and the domestic hot water load. Since these separate loads are almost always imbalanced, the heating greater than the water, or peak demand for DHW exceeds the design load for heating, it makes specifying the Excellence a little tricky. They can be great for a couple of showers but the only way to fill a large tub--more than 60 gallons--is with standing water sized to the load. Say the Triangle Tube 110 with a 60 gallon Smart Tank.

The reason you only experience the cold water in the winter is the domestic water you start with being colder in winter and it takes more heat to raise the temperature to the same level. This is a symptom of designing to close to the spec. The Excellence has a small storage tank on-board and will outperform any "tankless" water heater with a similar output since a little storage goes a long way. Like a tankless the Excellence Combi Boiler will keep up with a typical shower if the flow is restricted so the boiler can keep up--something tankless water heaters do automatically.

Performance, and reliability will suffer if the boiler is not serviced regularly by qualified technicians.

So what your saying is that the 14 gallon tank on it is not enough to keep up with the demand. i.e. i fill the tub with 14 gallons of water from the reserve and then it gets cold since it can't keep up with demand. Is there a way to configure it to keep up with this demand or am I out of luck due to the small reserve tank? And when you say smart tank, is this a tank not attached to the boiler but a separate system?

FYI, I don't remember this happening the first year but subsequent years (2-3) it's become more evident. It could have been from the warm winter we had that year, or that the system was "shut off" due to a leak in one of the radiators, i.e. lost settings?

What are next steps for me to support the demand in my home? Heating has never been an issue, however it's a situation where we "don't flush the toilet" around our house in the winter when the hot water is requested.